As a drive power source of the present mobile electronic apparatus, such as a mobile phone, a mobile personal computer, or a mobile music player, and furthermore, as a power source of a hybrid electric vehicle (HEV or PHEV) or an electric vehicle (EV), a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery having a high energy density and a high capacity has been widely used.
Since this nonaqueous electrolyte secondary battery itself generates heat when being used or charged, and in addition, since an apparatus using this nonaqueous electrolyte secondary battery also generates heat, the temperature thereof may be increased in some cases. In particular, when a plurality of nonaqueous electrolyte secondary batteries are collectively used as an assembled battery, heat is not uniformly dispersed, and the temperature may be locally increased in some cases. Hence, there has been desired a nonaqueous electrolyte secondary battery in which various types of battery characteristics are not degraded even in a high-temperature environment.
In order to improve various types of battery characteristics of the nonaqueous electrolyte secondary battery at a high temperature, various measures have been carried out. For example, the following Patent Document 1 has disclosed the invention of a nonaqueous electrolyte secondary battery in which in order to improve high-temperature charge storage characteristics, a protective layer containing alumina, silicon dioxide, zirconia, or a water-insoluble or a low-water soluble lithium salt is provided on at least one surface of a positive electrode plate and a negative electrode plate.
In addition, the following Patent Document 2 has disclosed the invention of a nonaqueous electrolyte secondary battery and a positive electrode active material in which in order to suppress a reaction between a positive electrode active material and a nonaqueous electrolyte solution at a high potential, a compound of an element of Group III of the periodic table is provided partially on the surfaces of positive electrode active material particles.